This invention relates to the manufacture of thermally expansive bimetallic members and more particularly to the manufacture of thermally expansive bimetallic members having snap action capabilities.
Thermally expansive bimetallic members incorporating a snap action response are primarily utilized in switching mechanisms of the thermostatic variety. Perhaps the best known of these devices are thermostatic switches which utilize a bimetallic material having low and high expanding sides joined together along a common interface. Snap action bimetallic switches typically possess two positions of stability with each of these positions responsive to an established temperature. When the temperature of the device is below one (the lower) of these established temperatures, the device is in one of the stable positions. Accordingly, as the ambient temperature about the member is raised to a second (higher) temperature, the thermally responsive member snaps to a second position of stability and remains in this position provided the temperature remains at or above this second level. Should the ambient temperature now be lowered to the first (lower) temperature, resulting in a corresponding lowering of the temperature of the member, the member will snap back to its original position. The difference in temperature between the two described temperatures corresponding to the respective positions of stability is known as the differential temperature.
A known method of manufacturing snap-action switches of the variety described has included a forming operation in which the thermally expansive member is positioned between two opposingly positioned shaping or die members with the members then being actuated to engage the expansive member to provide it with the desired configuration needed to achieve snap action. Such a configuration usually consists of a knee and/or corresponding bowed portion, a dimpled portion or portions, a series of ridges, etc. An example of this type of formation is described in U.S. Pat. No. 3,748,888 wherein a snap action bimetallic disc is provided with a series of scallops which serve as stiffening members. These members in turn are designed to limit the previously described differential temperature range of the bimetallic article.
While the above and similar methods have proven successful in reducing the differential temperature, none to date have been capable of varying the differential range of the articles during their manufacture without requiring rather extensive modifications to the equipment making the member or to the member itself. That is, there has never been developed a method capable of changing the snap action characteristics of consecutively produced thermally expansive members without requiring either a complete change in the defining die members or substantial modification thereto. Such alterations to the snap action characteristics are often necessitated as a result of varying operational requirements. For example, it may be desirous to produce a bimetallic snap action member having a differential temperature range of about 40.degree.F with an upper limit or "ON" temperature (2nd stable position) of 100.degree.F and a corresponding lower limit or "OFF" temperature (1st stable position) of 60.degree.F. To now provide a similar bimetallic member with an "ON" of 105.degree.F and an "OFF" of 65.degree.F has previously required a complete change in the defining die bodies or the thicknesses of the expansive members being formed. In effect, what is now produced is an entirely different bimetallic member. Further, to provide a second bimetallic member having similar thickness dimensions with a broader or more narrow differential range has necessitated the previously described modifications to the dies to provide deeper (or more narrow) dimples, scallops, etc. As can be appreciated, the above described changes have resulted in both added costs and time required to produce said articles.
It is believed therefore that an improved method for controlling the snap action characteristics of thermally expansive bimetallic members during their manufacture without requiring extensive modifications or changes in the equipment which provides these characteristics or in the configuration of the members themselves would constitute an advancement in the art.